Publications


Sensitivity of detachment extent to magnetic configuration and external parameters

Nuclear Fusion 56 (2016)

B Lipschultz, FI Parra, IH Hutchinson

© 2016 IAEA, Vienna.Divertor detachment may be essential to reduce heat loads to magnetic fusion tokamak reactor divertor surfaces. Yet in experiments it is difficult to control the extent of the detached, low pressure, plasma region. At maximum extent the front edge of the detached region reaches the X-point and can lead to degradation of core plasma properties. We define the 'detachment window' in a given position control variable C (for example, the upstream plasma density) as the range in C within which the front location can be stably held at any position from the target to the X-point; increased detachment window corresponds to better control. We extend a 1D analytic model [1] to determine the detachment window for the following control variables: the upstream plasma density, the impurity concentration and the power entering the scrape-off layer (SOL). We find that variations in magnetic configuration can have strong effects; increasing the ratio of the total magnetic field at the X-point to that at the target,Bx/Bt, (total flux expansion, as in the super-x divertor configuration) strongly increases the detachment window for all control variables studied, thus strongly improving detachment front control and the capability of the divertor plasma to passively accommodate transients while still staying detached. Increasing flux tube length and thus volume in the divertor, through poloidal flux expansion (as in the snowflake or x-divertor configurations) or length of the divertor, also increases the detachment window, but less than the total flux expansion does. The sensitivity of the detachment front location, zh, to each control variable, C, defined as , depends on the magnetic configuration. The size of the radiating volume and the total divertor radiation increase ∝ (Bx/Bt)2 and ∝ Bx/Bt, respectively, but not by increasing divertor poloidal flux expansion or field line length. We believe this model is applicable more generally to any thermal fronts in flux tubes with varying magnetic field, and similar sources and sinks, such as detachment fronts in stellarator divertors and solar prominences in coronal loops.


AN ALL-SKY SEARCH for THREE FLAVORS of NEUTRINOS from GAMMA-RAY BURSTS with the ICECUBE NEUTRINO OBSERVATORY

Astrophysical Journal 824 (2016)

MG Aartsen, K Abraham, M Ackermann, J Adams, JA Aguilar, M Ahlers, M Ahrens, D Altmann, T Anderson, I Ansseau, G Anton, M Archinger, C Arguelles, TC Arlen, J Auffenberg, X Bai, SW Barwick, V Baum, R Bay, JJ Beatty, JB Tjus, KH Becker, E Beiser, S Benzvi, P Berghaus, D Berley, E Bernardini, A Bernhard, DZ Besson, G Binder, D Bindig, M Bissok, E Blaufuss, J Blumenthal, DJ Boersma, C Bohm, M Börner, F Bos, D Bose, S Böser, O Botner, J Braun, L Brayeur, HP Bretz, N Buzinsky, J Casey, M Casier, E Cheung, D Chirkin, A Christov, K Clark, L Classen, S Coenders, GH Collin, JM Conrad, DF Cowen, AH Cruz Silva, J Daughhetee, JC Davis, M Day, JPAM De André, C De Clercq, E Del Pino Rosendo, H Dembinski, S De Ridder, P Desiati, KD De Vries, G De Wasseige, M De With, T Deyoung, JC Díaz-Vélez, V Di Lorenzo, H Dujmovic, JP Dumm, M Dunkman, B Eberhardt, T Ehrhardt, B Eichmann, S Euler, PA Evenson, S Fahey, AR Fazely, J Feintzeig, J Felde, K Filimonov, C Finley, S Flis, CC Fösig, T Fuchs, TK Gaisser, R Gaior, J Gallagher, L Gerhardt, K Ghorbani, D Gier, L Gladstone

© 2016. The American Astronomical Society. All rights reserved.We present the results and methodology of a search for neutrinos produced in the decay of charged pions created in interactions between protons and gamma-rays during the prompt emission of 807 gamma-ray bursts (GRBs) over the entire sky. This three-year search is the first in IceCube for shower-like Cherenkov light patterns from electron, muon, and tau neutrinos correlated with GRBs. We detect five low-significance events correlated with five GRBs. These events are consistent with the background expectation from atmospheric muons and neutrinos. The results of this search in combination with those of IceCube's four years of searches for track-like Cherenkov light patterns from muon neutrinos correlated with Northern-Hemisphere GRBs produce limits that tightly constrain current models of neutrino and ultra high energy cosmic ray production in GRB fireballs.


The prompt atmospheric neutrino flux in the light of LHCb

JOURNAL OF HIGH ENERGY PHYSICS (2016) ARTN 130

R Gauld, J Rojo, L Rottoli, S Sarkar, J Talbert


Parallel impurity dynamics in the TJ-II stellarator

Plasma Physics and Controlled Fusion 58 (2016)

JA Alonso, JL Velasco, I Calvo, T Estrada, JM Fontdecaba, JM García-Regaña, J Geiger, M Landreman, KJ McCarthy, F Medina, BP Van Milligen, MA Ochando, FI Parra

© 2016 IOP Publishing Ltd.We review in a tutorial fashion some of the causes of impurity density variations along field lines and radial impurity transport in the moment approach framework. An explicit and compact form of the parallel inertia force valid for arbitrary toroidal geometry and magnetic coordinates is derived and shown to be non-negligible for typical TJ-II plasma conditions. In the second part of the article, we apply the fluid model including main ion-impurity friction and inertia to observations of asymmetric emissivity patterns in neutral beam heated plasmas of the TJ-II stellarator. The model is able to explain qualitatively several features of the radiation asymmetry, both in stationary and transient conditions, based on the calculated in-surface variations of the impurity density.


A review of action estimation methods for galactic dynamics

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 457 (2016) 2107-2121

JL Sanders, J Binney


Numerical study of neutron beam divergence in a beam-fusion scenario employing laser driven ions

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 829 (2016) 176-180

A Alejo, A Green, H Ahmed, APL Robinson, M Cerchez, R Clarke, D Doria, S Dorkings, J Fernandez, P McKenna, SR Mirfayzi, K Naughton, D Neely, P Norreys, C Peth, H Powell, JA Ruiz, J Swain, O Willi, M Borghesi, S Kar

© 2016 Elsevier B.V.The most established route to create a laser-based neutron source is by employing laser accelerated, low atomic-number ions in fusion reactions. In addition to the high reaction cross-sections at moderate energies of the projectile ions, the anisotropy in neutron emission is another important feature of beam-fusion reactions. Using a simple numerical model based on neutron generation in a pitcher–catcher scenario, anisotropy in neutron emission was studied for the deuterium–deuterium fusion reaction. Simulation results are consistent with the narrow-divergence (∼70° full width at half maximum) neutron beam recently served in an experiment employing multi-MeV deuteron beams of narrow divergence (up to 30° FWHM, depending on the ion energy) accelerated by a sub-petawatt laser pulse from thin deuterated plastic foils via the Target Normal Sheath Acceleration mechanism. By varying the input ion beam parameters, simulations show that a further improvement in the neutron beam directionality (i.e. reduction in the beam divergence) can be obtained by increasing the projectile ion beam temperature and cut-off energy, as expected from interactions employing higher power lasers at upcoming facilities.


Measures of three-dimensional anisotropy and intermittency in strong Alfvénic turbulence

Monthly Notices of the Royal Astronomical Society 459 (2016) 2130-2139

A Mallet, AA Schekochihin, BDG Chandran, CHK Chen, TS Horbury, RT Wicks, CC Greenan

© 2016 The Authors.We measure the local anisotropy of numerically simulated strong Alfvénic turbulence with respect to two local, physically relevant directions: along the local mean magnetic field and along the local direction of one of the fluctuating Elsasser fields. We find significant scaling anisotropywith respect to both these directions: the fluctuations are 'ribbon-like' - statistically, they are elongated along both the mean magnetic field and the fluctuating field. The latter form of anisotropy is due to scale-dependent alignment of the fluctuating fields. The intermittent scalings of the nth-order conditional structure functions in the direction perpendicular to both the local mean field and the fluctuations agree well with the theory of Chandran, Schekochihin & Mallet, while the parallel scalings are consistent with those implied by the critical-balance conjecture. We quantify the relationship between the perpendicular scalings and those in the fluctuation and parallel directions, and find that the scaling exponent of the perpendicular anisotropy (i.e. of the aspect ratio of the Alfvénic structures in the plane perpendicular to the mean magnetic field) depends on the amplitude of the fluctuations. This is shown to be equivalent to the anticorrelation of fluctuation amplitude and alignment at each scale. The dependence of the anisotropy on amplitude is shown to be more significant for the anisotropy between the perpendicular and fluctuation-direction scales than it is between the perpendicular and parallel scales.


Determination of the shape and orientation of nonlinear magnetic structures measured by Cluster spacecraft in the vicinity of the bow shock

Journal of Geophysical Research A: Space Physics 121 (2016) 2390-2406

M Grzesiak, D Przepiórka, M Strumik, K Stasiewicz

© 2016. American Geophysical Union. All Rights Reserved.We present a new method of determination of the size and the orientation of nonlinear electromagnetic structures observed in space plasmas. The method is based on the analysis of covariance matrix of gradients of fields estimated from multipoint spacecraft measurements. It does not make use of Taylor hypothesis and gives fully three-dimensional estimates without assuming any symmetries of the structures. The method has been tested first on synthetic data and then applied to four-point Cluster spacecraft measurements to determine geometrical properties of nonlinear electromagnetic structures observed in the vicinity of the bow shock. These structures comprise ULF waves that steepen to form shocklets (short large-amplitude magnetic structures) in the foreshock region and large-amplitude mirror mode structures observed in the magnetosheath downstream of the bow shock. In the case of foreshock ULF waves we find the three-axis structure sizes of 1000, 3000, and 7000 km oriented to the ambient field at angles of 75, 30, and 60°, respectively. For the mirror modes our results give sizes of 150, 300, and 700 km oriented at angles close to the perpendicular direction for the shortest and middle scales and parallel orientation for the longest scale. The estimated geometry and properties of analyzed nonlinear structures follow, in general, those obtained previously.


Modelling the circumstellar medium in RS Ophiuchi and its link to Type Ia supernovae

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 457 (2016) 822-835

RA Booth, S Mohamed, P Podsiadlowski


Nanosecond formation of diamond and lonsdaleite by shock compression of graphite.

Nature communications 7 (2016) 10970-

D Kraus, A Ravasio, M Gauthier, DO Gericke, J Vorberger, S Frydrych, J Helfrich, LB Fletcher, G Schaumann, B Nagler, B Barbrel, B Bachmann, EJ Gamboa, S Göde, E Granados, G Gregori, HJ Lee, P Neumayer, W Schumaker, T Döppner, RW Falcone, SH Glenzer, M Roth

The shock-induced transition from graphite to diamond has been of great scientific and technological interest since the discovery of microscopic diamonds in remnants of explosively driven graphite. Furthermore, shock synthesis of diamond and lonsdaleite, a speculative hexagonal carbon polymorph with unique hardness, is expected to happen during violent meteor impacts. Here, we show unprecedented in situ X-ray diffraction measurements of diamond formation on nanosecond timescales by shock compression of pyrolytic as well as polycrystalline graphite to pressures from 19 GPa up to 228 GPa. While we observe the transition to diamond starting at 50 GPa for both pyrolytic and polycrystalline graphite, we also record the direct formation of lonsdaleite above 170 GPa for pyrolytic samples only. Our experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites.


Theory of density fluctuations in strongly radiative plasmas

PHYSICAL REVIEW E 93 (2016) ARTN 033201

JE Cross, P Mabey, DO Gericke, G Gregori


Characteristics of betatron radiation from direct-laser-accelerated electrons.

Physical review. E 93 (2016) 063203-

TW Huang, AP Robinson, CT Zhou, B Qiao, B Liu, SC Ruan, XT He, PA Norreys

Betatron radiation from direct-laser-accelerated electrons is characterized analytically and numerically. It is shown here that the electron dynamics is strongly dependent on a self-similar parameter S(≡n_{e}/n_{c}a_{0}). Both the electron transverse momentum and energy are proportional to the normalized amplitude of laser field (a_{0}) for a fixed value of S. As a result, the total number of radiated photons scales as a_{0}^{2}/sqrt[S] and the energy conversion efficiency of photons from the accelerated electrons scales as a_{0}^{3}/S. The particle-in-cell simulations agree well with the analytical scalings. It is suggested that a tunable high-energy and high-flux radiation source can be achieved by exploiting this regime.


The quiescent phase of galactic disc growth

Monthly Notices of the Royal Astronomical Society 459 (2016) 3326-3348

M Aumer, J Binney, R Schönrich

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.We perform a series of controlled N-body simulations of growing disc galaxies within non-growing, live dark matter haloes of varying mass and concentration. Our initial conditions include either a low-mass disc or a compact bulge. New stellar particles are continuously added on near-circular orbits to the existing disc, so spiral structure is continuously excited. To study the effect of combined spiral and giant molecular cloud (GMC) heating on the discs, we introduce massive, short-lived particles that sample a GMC mass function. An isothermal gas component is introduced for a subset of the models. We perform a resolution study and vary parameters governing the GMC population, the histories of star formation and radial scale growth. Models with GMCs and standard values for the disc mass and halo density provide the right level of self-gravity to explain the age-velocity dispersion relation of the solar neighbourhood (Snhd). GMC heating generates remarkably exponential vertical profiles with scaleheights that are radially constant and agree with observations of galactic thin discs. GMCs are also capable of significantly delaying bar formation. The amount of spiral-induced radial migration agrees with what is required for the metallicity distribution of the Snhd. However, in our standard models, the outward-migrating populations are not hot enough vertically to create thick discs. Thick discs can form in models with high baryon fractions, but the corresponding bars are too long, the young stellar populations too hot and the discs flare considerably.


Beamed neutron emission driven by laser accelerated light ions

New Journal of Physics 18 (2016)

S Kar, A Green, H Ahmed, A Alejo, APL Robinson, M Cerchez, R Clarke, D Doria, S Dorkings, J Fernandez, SR Mirfayzi, P McKenna, K Naughton, D Neely, P Norreys, C Peth, H Powell, JA Ruiz, J Swain, O Willi, M Borghesi

© 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.Highly anisotropic, beam-like neutron emission with peak flux of the order of 109 n/sr was obtained from light nuclei reactions in a pitcher-catcher scenario, by employing MeV ions driven by a subpetawatt laser. The spatial profile of the neutron beam, fully captured for the first time by employing a CR39 nuclear track detector, shows a FWHM divergence angle of ∼70°, with a peak flux nearly an order of magnitude higher than the isotropic component elsewhere. The observed beamed flux of neutrons is highly favourable for a wide range of applications, and indeed for further transport and moderation to thermal energies. A systematic study employing various combinations of pitcher-catcher materials indicates the dominant reactions being d(p, n+p)1 H and d(d,n)3He. Albeit insufficient cross-section data are available for modelling, the observed anisotropy in the neutrons' spatial and spectral profiles is most likely related to the directionality and high energy of the projectile ions.


Characteristics of betatron radiation from direct-laser-accelerated electrons

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics (2016)

PA Norreys


Theory of Thomson scattering in inhomogeneous media.

Scientific reports 6 (2016) 24283-

PM Kozlowski, BJ Crowley, DO Gericke, SP Regan, G Gregori

Thomson scattering of laser light is one of the most fundamental diagnostics of plasma density, temperature and magnetic fields. It relies on the assumption that the properties in the probed volume are homogeneous and constant during the probing time. On the other hand, laboratory plasmas are seldom uniform and homogeneous on the temporal and spatial dimensions over which data is collected. This is particularly true for laser-produced high-energy-density matter, which often exhibits steep gradients in temperature, density and pressure, on a scale determined by the laser focus. Here, we discuss the modification of the cross section for Thomson scattering in fully-ionized media exhibiting steep spatial inhomogeneities and/or fast temporal fluctuations. We show that the predicted Thomson scattering spectra are greatly altered compared to the uniform case, and may lead to violations of detailed balance. Therefore, careful interpretation of the spectra is necessary for spatially or temporally inhomogeneous systems.


Effect of the Shafranov shift and the gradient of β on intrinsic momentum transport in up-down asymmetric tokamaks

Plasma Physics and Controlled Fusion 58 (2016)

J Ball, FI Parra, J Lee, AJ Cerfon

© 2016 IOP Publishing Ltd Printed in the UK.Tokamaks with up-down asymmetric poloidal cross-sections spontaneously rotate due to turbulent transport of momentum. In this work, we investigate the effect of the Shafranov shift on this intrinsic rotation, primarily by analyzing tokamaks with tilted elliptical flux surfaces. By expanding the Grad-Shafranov equation in the large aspect ratio limit we calculate the magnitude and direction of the Shafranov shift in tilted elliptical tokamaks. The results show that, while the Shafranov shift becomes updown asymmetric and depends strongly on the tilt angle of the flux surfaces, it is insensitive to the shape of the current and pressure profiles (when the geometry, total plasma current, and average pressure gradient are kept fixed). Next, local nonlinear gyrokinetic simulations of these MHD equilibria are performed with GS2, which reveal that the Shafranov shift can significantly enhance the momentum transport. However, to be consistent, the effect of β′ (i.e. the radial gradient of β) on the magnetic equilibrium was also included, which was found to significantly reduce momentum transport. Including these two competing effects broadens the rotation profile, but leaves the on-axis value of the rotation roughly unchanged. Consequently, the shape of the β profile has a significant effect on the rotation profile of an up-down asymmetric tokamak.


SEARCH for SOURCES of HIGH-ENERGY NEUTRONS with FOUR YEARS of DATA from the ICETOP DETECTOR

Astrophysical Journal 830 (2016)

MG Aartsen, K Abraham, M Ackermann, J Adams, JA Aguilar, M Ahlers, M Ahrens, D Altmann, K Andeen, T Anderson, I Ansseau, G Anton, M Archinger, C Argüelles, J Auffenberg, S Axani, X Bai, SW Barwick, V Baum, R Bay, JJ Beatty, JB Tjus, KH Becker, S Benzvi, P Berghaus, D Berley, E Bernardini, A Bernhard, DZ Besson, G Binder, D Bindig, M Bissok, E Blaufuss, S Blot, C Bohm, M Börner, F Bos, D Bose, S Böser, O Botner, J Braun, L Brayeur, HP Bretz, A Burgman, T Carver, M Casier, E Cheung, D Chirkin, A Christov, K Clark, L Classen, S Coenders, GH Collin, JM Conrad, DF Cowen, R Cross, M Day, JPAMD André, CD Clercq, EDP Rosendo, H Dembinski, SD Ridder, P Desiati, KDD Vries, GD Wasseige, MD With, T Deyoung, JC Díaz-Vélez, VD Lorenzo, H Dujmovic, JP Dumm, M Dunkman, B Eberhardt, T Ehrhardt, B Eichmann, P Eller, S Euler, PA Evenson, S Fahey, AR Fazely, J Feintzeig, J Felde, K Filimonov, C Finley, S Flis, CC Fösig, A Franckowiak, E Friedman, T Fuchs, TK Gaisser, J Gallagher, L Gerhardt, K Ghorbani, W Giang, L Gladstone, M Glagla

© 2016. The American Astronomical Society. All rights reserved..IceTop is an air-shower array located on the Antarctic ice sheet at the geographic South Pole. IceTop can detect an astrophysical flux of neutrons from Galactic sources as an excess of cosmic-ray air showers arriving from the source direction. Neutrons are undeflected by the Galactic magnetic field and can typically travel 10 (E/PeV) pc before decay. Two searches are performed using 4 yr of the IceTop data set to look for a statistically significant excess of events with energies above 10 PeV (1016 eV) arriving within a small solid angle. The all-sky search method covers from -90° to approximately -50° in declination. No significant excess is found. A targeted search is also performed, looking for significant correlation with candidate sources in different target sets. This search uses a higher-energy cut (100 PeV) since most target objects lie beyond 1 kpc. The target sets include pulsars with confirmed TeV energy photon fluxes and high-mass X-ray binaries. No significant correlation is found for any target set. Flux upper limits are determined for both searches, which can constrain Galactic neutron sources and production scenarios.


Constraints on Ultrahigh-Energy Cosmic-Ray Sources from a Search for Neutrinos above 10 PeV with IceCube.

Phys Rev Lett 117 (2016) 241101-

MG Aartsen, K Abraham, M Ackermann, J Adams, JA Aguilar, M Ahlers, M Ahrens, D Altmann, K Andeen, T Anderson, I Ansseau, G Anton, M Archinger, C Argüelles, J Auffenberg, S Axani, X Bai, SW Barwick, V Baum, R Bay, JJ Beatty, J Becker Tjus, KH Becker, S BenZvi, P Berghaus, D Berley, E Bernardini, A Bernhard, DZ Besson, G Binder, D Bindig, M Bissok, E Blaufuss, S Blot, C Bohm, M Börner, F Bos, D Bose, S Böser, O Botner, J Braun, L Brayeur, HP Bretz, A Burgman, T Carver, M Casier, E Cheung, D Chirkin, A Christov, K Clark, L Classen, S Coenders, GH Collin, JM Conrad, DF Cowen, R Cross, M Day, JP de André, C De Clercq, E Del Pino Rosendo, H Dembinski, S De Ridder, P Desiati, KD de Vries, G de Wasseige, M de With, T DeYoung, JC Díaz-Vélez, V di Lorenzo, H Dujmovic, JP Dumm, M Dunkman, B Eberhardt, T Ehrhardt, B Eichmann, P Eller, S Euler, PA Evenson, S Fahey, AR Fazely, J Feintzeig, J Felde, K Filimonov, C Finley, S Flis, CC Fösig, A Franckowiak, E Friedman, T Fuchs, TK Gaisser, J Gallagher, L Gerhardt, K Ghorbani, W Giang, L Gladstone, M Glagla, T Glüsenkamp, A Goldschmidt, G Golup, JG Gonzalez, D Grant, Z Griffith, C Haack, A Haj Ismail, A Hallgren, F Halzen, E Hansen, B Hansmann, T Hansmann, K Hanson, D Hebecker, D Heereman, K Helbing, R Hellauer, S Hickford, J Hignight, GC Hill, KD Hoffman, R Hoffmann, K Holzapfel, K Hoshina, F Huang, M Huber, K Hultqvist, S In, A Ishihara, E Jacobi, GS Japaridze, M Jeong, K Jero, BJ Jones, M Jurkovic, A Kappes, T Karg, A Karle, U Katz, M Kauer, A Keivani, JL Kelley, J Kemp, A Kheirandish, M Kim, T Kintscher, J Kiryluk, T Kittler, SR Klein, G Kohnen, R Koirala, H Kolanoski, R Konietz, L Köpke, C Kopper, S Kopper, DJ Koskinen, M Kowalski, K Krings, M Kroll, G Krückl, C Krüger, J Kunnen, S Kunwar, N Kurahashi, T Kuwabara, M Labare, JL Lanfranchi, MJ Larson, F Lauber, D Lennarz, M Lesiak-Bzdak, M Leuermann, J Leuner, L Lu, J Lünemann, J Madsen, G Maggi, KB Mahn, S Mancina, M Mandelartz, R Maruyama, K Mase, R Maunu, F McNally, K Meagher, M Medici, M Meier, A Meli, T Menne, G Merino, T Meures, S Miarecki, L Mohrmann, T Montaruli, M Moulai, R Nahnhauer, U Naumann, G Neer, H Niederhausen, SC Nowicki, DR Nygren, A Obertacke Pollmann, A Olivas, A O'Murchadha, T Palczewski, H Pandya, DV Pankova, Ö Penek, JA Pepper, C Pérez de Los Heros, D Pieloth, E Pinat, PB Price, GT Przybylski, M Quinnan, C Raab, L Rädel, M Rameez, K Rawlins, R Reimann, B Relethford, M Relich, E Resconi, W Rhode, M Richman, B Riedel, S Robertson, M Rongen, C Rott, T Ruhe, D Ryckbosch, D Rysewyk, L Sabbatini, SE Sanchez Herrera, A Sandrock, J Sandroos, S Sarkar, K Satalecka, M Schimp, P Schlunder, T Schmidt, S Schoenen, S Schöneberg, L Schumacher, D Seckel, S Seunarine, D Soldin, M Song, GM Spiczak, C Spiering, M Stahlberg, T Stanev, A Stasik, A Steuer, T Stezelberger, RG Stokstad, A Stößl, R Ström, NL Strotjohann, GW Sullivan, M Sutherland, H Taavola, I Taboada, J Tatar, F Tenholt, S Ter-Antonyan, A Terliuk, G Tešić, S Tilav, PA Toale, MN Tobin, S Toscano, D Tosi, M Tselengidou, A Turcati, E Unger, M Usner, J Vandenbroucke, N van Eijndhoven, S Vanheule, M van Rossem, J van Santen, J Veenkamp, M Vehring, M Voge, M Vraeghe, C Walck, A Wallace, M Wallraff, N Wandkowsky, C Weaver, MJ Weiss, C Wendt, S Westerhoff, BJ Whelan, S Wickmann, K Wiebe, CH Wiebusch, L Wille, DR Williams, L Wills, M Wolf, TR Wood, E Woolsey, K Woschnagg, DL Xu, XW Xu, Y Xu, JP Yanez, G Yodh, S Yoshida, M Zoll, IceCube Collaboration

We report constraints on the sources of ultrahigh-energy cosmic rays (UHECRs) above 10^{9}  GeV, based on an analysis of seven years of IceCube data. This analysis efficiently selects very high- energy neutrino-induced events which have deposited energies from 5×10^{5}  GeV to above 10^{11}  GeV. Two neutrino-induced events with an estimated deposited energy of (2.6±0.3)×10^{6}  GeV, the highest neutrino energy observed so far, and (7.7±2.0)×10^{5}  GeV were detected. The atmospheric background-only hypothesis of detecting these events is rejected at 3.6σ. The hypothesis that the observed events are of cosmogenic origin is also rejected at >99% CL because of the limited deposited energy and the nonobservation of events at higher energy, while their observation is consistent with an astrophysical origin. Our limits on cosmogenic neutrino fluxes disfavor the UHECR sources having a cosmological evolution stronger than the star formation rate, e.g., active galactic nuclei and γ-ray bursts, assuming proton-dominated UHECRs. Constraints on UHECR sources including mixed and heavy UHECR compositions are obtained for models of neutrino production within UHECR sources. Our limit disfavors a significant part of parameter space for active galactic nuclei and new-born pulsar models. These limits on the ultrahigh-energy neutrino flux models are the most stringent to date.


OBSERVATION and CHARACTERIZATION of A COSMIC MUON NEUTRINO FLUX from the NORTHERN HEMISPHERE USING SIX YEARS of ICECUBE DATA

Astrophysical Journal 833 (2016)

MG Aartsen, K Abraham, M Ackermann, J Adams, JA Aguilar, M Ahlers, M Ahrens, D Altmann, K Andeen, T Anderson, I Ansseau, G Anton, M Archinger, C Argüelles, J Auffenberg, S Axani, X Bai, SW Barwick, V Baum, R Bay, JJ Beatty, JB Tjus, KH Becker, S Benzvi, P Berghaus, D Berley, E Bernardini, A Bernhard, DZ Besson, G Binder, D Bindig, M Bissok, E Blaufuss, S Blot, C Bohm, M Börner, F Bos, D Bose, S Böser, O Botner, J Braun, L Brayeur, HP Bretz, A Burgman, T Carver, M Casier, E Cheung, D Chirkin, A Christov, K Clark, L Classen, S Coenders, GH Collin, JM Conrad, DF Cowen, R Cross, M Day, JPAMD André, CD Clercq, EDP Rosendo, H Dembinski, SD Ridder, P Desiati, KDD Vries, GD Wasseige, MD With, T Deyoung, JC Díaz-Vélez, VD Lorenzo, H Dujmovic, JP Dumm, M Dunkman, B Eberhardt, T Ehrhardt, B Eichmann, P Eller, S Euler, PA Evenson, S Fahey, AR Fazely, J Feintzeig, J Felde, K Filimonov, C Finley, S Flis, CC Fösig, A Franckowiak, E Friedman, T Fuchs, TK Gaisser, J Gallagher, L Gerhardt, K Ghorbani, W Giang, L Gladstone, M Glagla

© 2016. The American Astronomical Society. All rights reserved.The IceCube Collaboration has previously discovered a high-energy astrophysical neutrino flux using neutrino events with interaction vertices contained within the instrumented volume of the IceCube detector. We present a complementary measurement using charged current muon neutrino events where the interaction vertex can be outside this volume. As a consequence of the large muon range the effective area is significantly larger but the field of view is restricted to the Northern Hemisphere. IceCube data from 2009 through 2015 have been analyzed using a likelihood approach based on the reconstructed muon energy and zenith angle. At the highest neutrino energies between 194 TeV and 7.8 PeV a significant astrophysical contribution is observed, excluding a purely atmospheric origin of these events at 5.6s significance. The data are well described by an isotropic, unbroken power-law flux with a normalization at 100 TeV neutrino energy of (0.90 -0.27+0.30) × 10-18 Gev-1 cm-2 s-1 sr-1and a hard spectral index of γ = 2.13 ± 0.13. The observed spectrum is harder in comparison to previous IceCube analyses with lower energy thresholds which may indicate a break in the astrophysical neutrino spectrum of unknown origin. The highest-energy event observed has a reconstructed muon energy of (4.5 ± 1.2) PeV which implies a probability of less than 0.005% for this event to be of atmospheric origin. Analyzing the arrival directions of all events with reconstructed muon energies above 200 TeV no correlation with known γ-ray sources was found. Using the high statistics of atmospheric neutrinos we report the current best constraints on a prompt atmospheric muon neutrino flux originating from charmed meson decays which is below 1.06 in units of the flux normalization of the model in Enberg et al.

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